Traditionally, in a telecommunications network, users' or customers' premises are connected to a Public Switched Telephone Network (PSTN) by a lead-in cable consisting of either one or two pairs of copper conductors (wires). The lead-in cable is routed to a dwelling or other premises either aerially, in the case of an aerial Customer Access Network (CAN), or underground for the more recently deployed underground CANs.
Generally, new estates and residential developments now deploy cable underground. The cable is routed from a distribution point near a property boundary via a small plastic conduit to an entry point to a dwelling. The entry point is typically located at a convenient position, such as close to the electrical cable entry (meter box) or at some other point where access to the building is relatively straightforward.
The lead-in cable is generally pulled through the conduit, which has, for example, an internal diameter of about 20 mm, by means of a thin cord. The cord is threaded through the conduit by first pushing a rigid rod through a length of conduit, e.g. 4.5 m long, (rodding process) with the rope attached at one end. Having performed the rodding process it is then a simple matter to tie the rope to the end of the lead-in cable by means of a knot and then use the rope to haul the cable into and through the conduit. Most often the conduit does not form a completely straight line, but typically undulates and bends with a number of bend elements often being permitted with a radius of curvature generally down to about 100 mm.
There is an emerging need to replace copper conductor lead-in cable with fibre optic lead-in cable to provide users or customers with a range of new or improved services, such as Video on Demand (VoD), high speed Internet access, as well as telephone services over a single integrated network.
In the case of copper lead-in cable, the connection to the customer's equipment, whether the equipment is a standard telephone or a Digital Subscriber Line (DSL) modem, is straightforward and easily accomplished in the field with simple hand tools. The process may involve fitting a connector with screw terminals or, more likely, fitting a connector that can be secured by means of a simple hand operated crimping tool similar to a pair of pliers.
With the move to fibre optic systems the whole process becomes potentially far more complicated. While the fibre optic cable, and in particular the fibre, is very flexible, the fibre optic cable cannot be tied to a hauling rope without fracturing the fibre or, at best, severely affecting the fibre's transmission characteristics. The connection to the Optical Network Unit (ONT) that effectively forms the interface from the new generation PSTN and the customer's equipment requires a fibre to fibre connection to be made.
The fibre used in these systems is typically single-mode. Typically, the single-mode fibre has a mode field diameter (the part of the fibre that carries the signal) of about 9 microns. To obtain a good and reliable transmission it is necessary to butt two fibres together with sufficient precision such that the two extremely small mode fields align exactly. This process is typically accomplished in one of two ways. A direct fusion splice may be used whereby the two fibre ends are mounted in a complicated, high precision, fusion splicing machine that, using an electric arc, melts the two fibre end faces and fuses them together as one. Alternatively, an optical connector can be mounted on the end of each fibre and simply plugged together. Based on presently known technology, it is expensive and complicated to fit a connector to a fibre optic cable in the field since the mating components of the connector have to be machined after fitting to the fibre to ensure perfect alignment. Furthermore, the end face of the connector has to be polished to minimise losses.
Some forms of cable hauling attachments are presently known in the art.
Document WO 2006/021055, in the name of the present Applicant, discloses a hauling shroud for hauling a fibre optic cable along a conduit. The hauling shroud disclosed in said document includes a cavity to receive an optic connector. Moreover, the hauling shroud is provided with a locking mechanism which is obtained by the combination of a recess in the hauling shroud housing and a crimp lug to be received into the hauling shroud housing, the crimp lug being held in place by a retaining sleeve which is in threaded engagement with a retaining thread. The crimp lug is attached to at least one strengthening element, thereby removably holding the strengthening element, and thus the cable, to the hauling shroud. Therefore, the strengthening element is locked to the shroud body and retained in or by the locking mechanism. Furthermore, document WO 2006/021055 discloses an embodiment where the connector is part of a modular connector, for example a connector having a central body (ferrule) to which the optic fibre is fitted and is enclosed in the hauling shroud. An outer part of the connector then links with a mating part on the central body when it is to be optically joined.
Document U.S. Pat. No. 5,863,083 discloses a pulling grip which includes an elongated, flexible pulling grip housing for use in installing fibre optic cable and, more particularly, for installing a fibre optic cable which contains a number of pre-connectorized optical fibres. The pulling grip housing includes first and second portions which mate to form the pulling grip housing and which open to provide access to an internal cavity for placement of the pre-connectorized optical fibres of the fibre optic cable. The pulling grip housing can secure the connectors within the internal cavity to prevent undesirable tangling of the optical fibres during installation. For example, the pulling grip housing can include an adhesive surface or a number of slots for retaining respective ones of the connectors. The pulling grip is also connected to an end portion of the fibre optic cable and, more particularly, a strength element of the fibre optic cable such that forces imparted during the advancement of the pulling grip housing through a conduit are transferred to the strength element of the fibre optic cable and do not place undesirable strain on the optical fibres. The pulling grip housing therefore protects the optical fibres and the respective connectors from damage during installation while permitting pre-connectorized fibre optic cables to be installed regardless of the leg lengths of the optical fibres.
Document U.S. Pat. No. 5,129,027 discloses a drawing head for ribbon type optical cables equipped with respective end connectors. The drawing head comprises a drawing member connected at one end thereof to the axial strength member of the cable and at the other end thereof to a pulling grasping member, the drawing member being surrounded by a slotted body which has a length corresponding to a predetermined excess value of the fibre ribbon length and being provided with grooves adapted to accommodate the fibre ribbons disposed in alignment with the grooves of the slotted cable core. The slotted body is followed by a deformable support body which surrounds the drawing member and is provided with longitudinally separated and aligned housings which are designed to receive the end connectors of the ribbons. An aramid cable layer is locked between two sleeves possessed by the drawing head so that the pulling loads applied to the cable are distributed among the outer sheath, aramid layer and axial strength member of the optical cable.
Document U.S. Pat. No. 5,039,196 discloses a device for pulling optical fibre cables through cable ducts. Referring to FIG. 1a, an optical fibre cable 10 used with a pulling eye has a plurality of radial strength yarn threads 16 and steel armour layer 18. There is also provided diametrically opposed strength members 24. In a first embodiment, cable strength members 24 are slid by a user through the open end of the cable crimping sleeve portion 30 and into the longitudinally directed cavities 33 to be gripped via set-screws 34. In a second embodiment, two collets 52 (see FIG. 8) are designed to grip cable strength members 24. The use of the pulling eye assembly allows a multiple strength member cable to be pulled through cable ducts while protecting the fibres in the cable.
Document U.S. Pat. No. 5,013,125 discloses a pulling assembly for connectorized optical fibre cables. The pulling assembly is formed of a flexible metal braided hose portion for conveying a pulling force to said cable and for providing a chamber in which the cable connectors may be housed during a cable pulling operation. A cylindrical housing is attached to one end of said braided metal hose and includes a concentrically-arranged central strength member gripping apparatus and a buffer tube alignment structure disposed about the central strength member gripping apparatus. A crimping sleeve is attached to an opposite end of said cylindrical housing fixing said concentric arrangement within the cylindrical housing and being crimpably engageable with an outer surface of an optical fibre cable.
Document U.S. Pat. No. 4,684,211 discloses a device for pulling a fibre optic cable through ducts and conduits. Said device comprises an elongated housing having a closed forward end, an open rearward end, and a central bore extending longitudinally there through for reception of a pre-terminated fibre optic cable including one or more ferrules terminated in corresponding ferrules which rest within the housing, the forward end being provided with grasping means, and the rearward end being adapted for mounting to a tensile load-bearing portion of the terminated end of the fibre optic cable. In a preferred embodiment, the rearward end is provided with threads for threaded engagement with a receptor nut mounted on the strain relief of a terminated fibre optic cable.
Document U.S. Pat. No. 5,807,026 discloses an assembly for pulling the end of a cable. Said assembly includes a hollow anchoring body having an axial passage formed in a front end thereof for receiving an end of the cable. The anchoring body has an integral hollow cylindrical skirt coaxially extending rearwardly, the skirt receiving an axially positioned insulating ring and a clamping assembly that is located radially inwardly of the ring. The clamping assembly has three sections: (a) a hollow sleeve having an internal thread at a rear end thereof and a tapered shoulder at a front end thereof; (b) a clamping member received in the tapered shoulder of the sleeve; (c) a fastener screwed into the internal thread and abutting the clamping member; and (d) a head formed on the fastener to permit it to be screwed into the thread and apply axial pressure to the clamping member thereby forcing the clamping member to clamp the covering of an optical module of the cable. A removable hollow pulling cover axially abuts the anchoring body and covers the cylindrical skirt. A terminal plate located at an end of the hollow casing, opposite the cylindrical skirt, connects stripped fibres thereto. The anchoring body comprises a front part in which are provided holes which are suitable for receiving locking screws for the metal wires of the cable outer sheathing.
The Applicant has faced the problem of providing a hauling shroud as well as a cable termination and methods of hauling a cable along a conduit which can eliminate, or at least remarkably reduce, the problems that arise in seeking to deploy a fibre optic lead-in cable by using the known technology mentioned above. Principally, these problems include:    (i) Presently known optical lead-in cables do not lend themselves to traditional installation methods since they cannot be hauled in the conventional way.    (ii) Connection of the optical lead-in cable to the ONT is relatively complicated.    (iii) The use of fusion splicing to connect to the ONT requires highly trained operators with complicated and expensive equipment that is not easily portable to the various locations where the splice is required.    (iv) It is not easily possible to fit optical connectors with the required level of performance in the field.    (v) The conduit from the distribution point to a customer's premises is small, often being about 20 mm in diameter, and the conduit is not straight in most installations.    (vi) The development of a new estate is typically ad hoc in that, once the sub-divisions are approved, the infrastructure services are then installed. This typically means that electricity, water, gas and telecommunications services are pre-installed along the streets. At the time of installation it is required to pre-provision for each customer's requirements. There may then be anything up to perhaps 2-3 years before a customer's dwelling is built. This means that it is therefore necessary to be able to sufficiently protect the fibre optic lead-in cable, and in particular the fibre end with a factory, pre-connected or pre-fitted connector attached, for at least this period of time from water (pits usually become flooded), dirt or other environmental conditions.
In particular, in the case a pre-connectorized fibre optic cable is requested to be hauled along a conduit, in order to avoid that the forces imparted during pulling of the cable negatively affect the optical fibres thereof, the Applicant has noted that the known hauling systems mentioned above transfer said forces to a cable strength member by interposing said strength member between at least two substantially cylindrical elements, thereby providing a concentric multi-layered structure inside of which the cable strength member is arranged.
The Applicant has perceived that such a concentric multi-layered structure contributes in increasing the hauling shroud size in the radial direction, thereby negatively affecting—and sometimes even preventing—a correct and effective pulling of a pre-connectorized cable along a conduit, in particular when the latter has a very small inner diameter (e.g. even lower than 20 mm) and is provided with bends (having a curvature radius even down to about 100 mm) along the longitudinal development thereof.